Arrangement in a circulation lubrication system

ABSTRACT

An arrangement in a circulation lubrication system include a lubricating oil tank, pressure pipe lines for supplying oil to parts to be lubricated, return pipe lines for returning the oil from the parts to be lubricated to the oil tank, and a mechanism configured to pump oil into the pressure pipe lines and maintaining a desired state of lubrication. The mechanism configured to pump the oil into the pressure pipe lines may include a circulation lubrication pump and a suction duct through which the lubricating oil flows out of a lubricating oil tank, an underpressure tank coupled to the suction duct leading off from the lubricating oil tank, to the suction side of the circulation lubrication pump. The underpressure tank is a tank which allows the water contained in the oil to evaporate. To prevent cavitation of the circulation lubrication pump, the underpressure tank is placed substantially higher than the lubricating oil tank.

This application is the national phase of international applicationPCT/FI98/00121 filed Feb. 11, 1998 which designated the U.S.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an arrangement in a circulation lubricationsystem comprising a lubricating oil tank; pressure pipe lines forsupplying oil to parts to be lubricated; return pipe lines for returningthe oil from the parts to be lubricated to the oil tank; and means forpumping the oil into the pressure pipe lines and maintaining a desiredstate of lubrication, the means for pumping the oil into the pressurepipe lines comprising a circulation lubrication pump and a suction ductthrough which the lubricating oil is arranged to flow out of thelubricating oil tank.

2. Description of the Related Art

Circulation lubrication systems are today used widely to lubricatevarious machines especially when the lubricant is used for cooling theparts to be lubricated. An example of the use of circulation lubricationis the lubrication of the bearings of the drying cylinders in papermachines or the lubrication of gas turbines. In both cases the bearingsare subject to a thermal load from the outside.

Circulation lubrication is also used when the part to be lubricatedcreates considerable dissipation power. One example of such applicationsis the lubrication of gear boxes.

Still another use of circulation lubrication is in cases where thelubricant may get dirty in the part to be lubricated, and it should bepossible to reuse the lubricant after cleaning.

A circulation lubrication system usually comprises a pump operated by anelectric motor. The pump brings the oil into motion. The output of thepump is usually selected so that it exceeds the required flow rate by 10to 20%, so that a sufficient operating margin is left for the control ofbypass pressure. Oil is arranged to pass through replaceable filters.The filters are often arranged in two groups so that one group can beseparated by means of valves and the filters can be changed withouthaving to stop the entire assembly. An electric or steam-operated heateris often used for further heating the oil. The oil is cooled by a heatexchanger having water or air cooling means. The cooling power isadjusted by a temperature regulator provided for supply oil. The setvalue of the temperature regulator is often typically about 55° C.Pressure control is often effected by a bypass valve back to the oiltank. Depending on the system, the set values of the pressure controllertypically vary between 5 and 20 bar.

Oil is supplied to parts needing lubrication, such as different parts inpaper machine, by means of pressure trunk pipes usually made ofrustproof material. The oil flows in the pipes as a laminar flow, and sothe pressure drop is small. From the trunk pipes the oil is distributedto a plurality of flow metering boards wherefrom it is divided intorising pipes to be supplied to a number of parts to be lubricated. Fromthese parts the oil is passed through return pipes by utilizinggravitation into collector pipes on the return side. The oil is passedunder the influence of gravitation through the collector pipes into thetank of the circulation lubrication assembly. The pipes on the returnside are never full of oil. The inclination of the pipes is about 2 to3% towards the tank of the assembly. Before the tank the return oil ispassed through a coarse-mesh filter. The oil returned into the tank isthen again sucked into circulation by the pump. The dimensions of thetank are usually such that the oil stays in the tank for a certainperiod of time depending on the viscosity of the oil.

In the system the lubricating oil tank has several functions forconditioning the oil before recirculation. One function of the tank isto allow air bubbles contained in the oil to rise to the surface. Airbubbles may increase the liability of the pump to cavitation, and theymay deteriorate the lubricating film formed on the part needinglubrication. Another function is to allow large dirt particles withdensity considerably higher than that of oil to deposit on the bottom ofthe tank. To some extent water drops contained in the oil will also falldown in the tank. The density of water is so close to that of oil thatthe falling speed is slow. The tank condenses moist air flowing in thereturn pipes on the tank walls and drains the water along the walls,thus collecting it on the bottom of the tank. The tank also cools theoil through the walls. Furthermore, the tank forms a space into whichthe pipe lines are emptied at system shutdowns, and the tank serves asan oil storage in case of a pipe leakage, so that the machine to belubricated can be shut down controllably. Still another function of thepump is to make sure that there is always oil in the pump suction meansin order that air would not be sucked along. The moisture and suitabletemperature also enable bacteria to grow in the tank.

The tank also comprises thermostat-controlled oil heaters, which may beeither electric or steam-operated heaters. The heaters are used to heatthe great amount of oil contained in the oil tank within 4 to 8 hourstypically to about 55° C. before the system is started as the screwpumps used are not able to pump cold oil of high viscosity at full powerwithout the risk of cavitation.

Present circulation lubrication oil tanks have had similar basicsolutions for decades. A tank is basically a rectangle, the capacity ofwhich may typically vary from a few hundred liters up to 30 cubicmeters. The size required depends on the operating principle of thetanks, according to which principle, to keep in good condition, the oilmust be allowed to rest in the tank about 30 minutes, so that impuritiescontained in the oil could be separated before the oil is recirculated.In addition to storing the oil, the tank must also cool the oil and beable to separate air, water and other impurities from the oil as statedabove.

Because of their big size, the previously used tanks are often difficultto place in connection with machinery needing lubrication. Furthermore,a great amount of oil involves great investments, and especially today,it also involves a fire load, brought about by a great capacity, withother environmental risks. In practice, measurements have also provedthat despite the big size of the tank only a small portion of thecapacity of the tank is efficiently involved in the oil circulation.When the function of the flow fields is measured by calculating coursesof particles without a mass, the same phenomenon is observed alsonumerically. In a typical conventional tank provided with partitionwalls the operating efficiency is only 35 to 44%, which indicates theactual flow-through time in proportion to the theoretical flow-throughtime. In practice, for example a tank of 8 cubic meters, in which 350liters of oil flow per minute, has the theoretical flow-through time of22 minutes 52 seconds, in which time the amount of oil would go oncethrough the system. In reality however, warm oil entering the tank tendsto form internal flow channels inside the tank due to differences in theviscosity of oil. These channels make the contents of the tank formwalls in a stationary oil mass and a main flow-through channel formed inthe oil mass. In reality, the theoretical flow-through time of 22minutes 52 seconds is now in a range of 8 to 10 minutes, which isdefinitely too short. In addition to channeling, the flow field ofpreviously known tanks is also subject to heavy whirl forming, whichmakes the separation of dirt particles difficult. Channeling resultsfrom high flow rates in the tank.

To enhance the conditioning of oil, the oil capacity is alsounderpressurized. It is generally known to separate water from oil bymeans of underpressure, so that water contained in the oil evaporatesand can be discharged. The performances of commercially availableunderpressurizers are within a range of 0 to 20 liters per minute, dueto which this kind of device can only be connected with a by-circulationof the tank. The flow capacities of the present circulation lubricationsystems are typically several hundreds of liters per minute, so theperformance of an evaporator connected with the by-circulation remainsinsufficient.

SUMMARY OF THE INVENTION

The invention relates to the conditioning of oil and especially to theconditioning of oil by means of underpressure. The object of theinvention is to provide an arrangement by means of which the drawbacksof the prior art can be eliminated, i.e. water can be separated from thelubricating oil as efficiently as possible. This is achieved by means ofan arrangement according to the invention, which is characterized inthat to a suction duct leading off from the lubricating oil tank, to thesuction side of a circulation lubrication pump, is attached anunderpressure tank that is placed substantially higher than thelubricating oil tank, and that comprises means for discharging waterallows the water contained in the oil to evaporate.

The primary advantage of the invention is that it allows very efficientconditioning of the oil, so that the water contained in the oil can beseparated efficiently from the oil in a very simple manner. A furtheradvantage of the invention is that it is simple to carry out, and so itsintroduction and use are economical. Another advantage of the inventionis that it can be applied to various lubricating oil tanks already inuse, so that the conditioning of oil in old lubrication systems can beenhanced without substantial investment costs.

DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the following the invention will be described more closely by meansof a preferred embodiment shown in the attached drawing, wherein

FIG. 1 is a general view of a circulation lubrication system for a papermachine, and

FIG. 2 is a general view of an arrangement according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a general view of a circulation lubrication system for a papermachine. The reference numeral 1 indicates generally an oil tank and thereference numeral 2 indicates generally an assembly comprising pumps,filters and other similar devices. The reference numeral 3 showspressure pipe lines for supplying oil used as a lubricant to parts 4 tobe lubricated, in this special case to drying cylinders in the papermachine. Further in FIG. 1, the reference numeral 5 indicates returnpipe lines for returning the oil from the parts to be lubricated to theoil tank 1. The structure and operation of the system shown in FIG. 1are obvious to one skilled in the art, so these matters will not bedescribed more closely herein. The functions of the oil tank 1 have beendescribed above.

FIG. 2 shows a solution of the arrangement according to the invention.In FIG. 2, like reference numerals indicate correspondingly as in FIG.1. The aim of the solution shown in FIG. 2 is to enhance theconditioning of the oil by underpressurizing the oil capacity asdescribed above. Underpressurizing is not new as such in theconditioning of oil, but previously underpressurizing has not beenimplemented in the manner described in FIG. 2.

As stated here above, it is previously known to separate water from oilby means of underpressure, so that the water contained in the oilevaporates and can be discharged. However, the performances of thecommercially available underpressurizers are so poor that they can onlybe attached to a by-circulation of the lubricating oil tank. The flowcapacities of present circulation lubrication systems are so great thatthe performance of an evaporator attached to a by-circulation remainsinsufficient. The greater the negative pressure, or the lower theabsolute pressure, the better water evaporates from oil. The mostefficient solution of discharging water is achieved, if the entire flowcapacity in use can be underpressurized. In the arrangement shown inFIG. 2 the underpressure is maximized, and so the entire oil mass inflow is subjected to underpressure and evaporation.

In FIG. 2 the reference numeral 19 indicates an underpressure tank andthe reference numeral 20 indicates a circulation lubrication pump. Theunderpressure tank 19 is attached to the suction side of the circulationlubrication pump 20, to a pipe connected to a suction duct 12, whichunderpressure tank is placed substantially higher than the lubricatingoil tank 1. In the underpressure tank 19 a negative pressure isproduced, by means of which the oil is sucked out of a tank 1 into theunderpressure tank 19. The negative pressure can be produced by anyknown means. For example, the negative pressure can be achieved by meansof an underpressure pump. The underpressure pump must produce a negativepressure of at least 0.8 bar to vaporize the water contained in the oil.For example, blade wheel pumps have been used as an underpressure pumpin the pressure range of 0.1 to 10⁵ Pa. Other typical solutions are arotating pump, a liquid ring pump and a so called runner pump. Differentunderpressure pumps and, in general, solutions for producing a negativepressure are obvious to one skilled in the art, so these matters willnot be described more closely herein.

In an arrangement according to the invention the water contained in theoil evaporates in an underpressure tank 19. The underpressure tank alsocomprises means 21 for discharging the evaporated water from theunderpressure tank 19. The underpressurized oil flows through theunderpressure tank 19 to a sucking circulation lubrication pump 20 andfurther through the pump to the parts to be lubricated. The oil ispassed through pressure pipe lines 3 to the parts to be lubricated bymeans of the circulation lubrication pump 20. The oil returns from theparts to be lubricated to the lubricating oil tank 1 through return pipelines 5. The oil is conditioned before recirculation by means of thearrangement shown in FIG. 2, i.e. by means of the lubricating oil tank 1and the underpressure tank 19 as described here above.

Installing the underpressure equipment substantially higher than thelubricating oil tank allows the use of the optimal maximum underpressurewithout that the suction capacity of the pump is disturbed. Thedifference in altitude between the underpressure tank 19 and the suctionduct 20 of the tank is essential to the operation. If there were nodifference in altitude, the suction power of the pump would not besufficient against the underpressure provided for evaporation, in whichcase the pump would cavitate. In the arrangement shown in FIG. 2 themaximal underpressure can be achieved and the pump will maintain itssuction power due to the difference in the oil level in a suction line22.

The above embodiments are by no means intended to restrict theinvention, but the invention can be modified quite freely within thescope of the claims. Accordingly, it is obvious that the arrangementsaccording to the invention or its details need not necessarily besimilar to those shown in the figures but other solutions are possibleas well. As stated above, the negative pressure in the underpressuretank can be produced in any previously known manner. The lubricating oiltank may also have any kind of structure, since the invention can beapplied in connection with different lubricating oil tanks.

What is claimed is:
 1. A circulation lubrication system comprising: alubricating oil tank; pressure pipe lines configured to supply oil tothe part to be lubricated; return pipe lines configured to return theoil from the part to be lubricated to the oil tank; a mechanismconfigured to pump the oil into the pressure pipe lines and maintain adesired state of lubrication, the oil pumping mechanism including acirculation lubrication pump and a suction duct configured to convey thelubricating oil to flow out of the lubricating oil tank, anunderpressure tank coupled to the suction duct and the lubricating oiltank to a suction side of the circulation lubrication pump; a mechanismconfigured to discharge water evaporated from the oil in theunderpressure tank; and a suction line coupling the circulationlubrication pump, the underpressure tank and the lubricating oil tank,wherein, the underpressure tank is configured to allow water containedin the oil to evaporate, and the underpressure tank is placedsubstantially higher than the lubricating oil tank such that cavitationof the circulation lubrication pump is prevented, wherein a negativepressure is produced in the underpressure tank which sucks oil containedin the lubricating oil tank into the underpressure tank.
 2. Thecirculation lubrication system of claim 1, wherein an entire amount ofoil mass used in the circulation lubrication system is subject tounderpressure and evaporation.
 3. The circulation lubrication system ofclaim 1, wherein the negative pressure is at least 0.8 bar.
 4. Thecirculation lubrication system of claim 1, wherein water contained inthe oil evaporates in the underpressure tank.
 5. The circulationlubrication system of claim 1, wherein a maximal underpressure isachieved and the circulation lubrication pump maintains its suctionpower due to a difference in oil level in a suction line.
 6. Thecirculation lubrication system of claim 1, wherein oil flowing throughthe circulation lubrication system is conditioned by the lubricating oiltank and the underpressure tank after the oil is used to lubricate thepart.